1. Field of the Invention
The present invention relates generally to dispensing payloads such as chaff from rockets, mortars, bombs, gun projectiles and the like and more specifically, to an apparatus and method for dispensing and disseminating chaff or other payloads by generating pressurized gas or steam.
2. Prior Art
Chaff has been employed as a radar interdiction countermeasure ever since shredded aluminum foil called "window" was thrown from combat aircraft during World War II. Such electrically conductive material reflects multiple frequencies of the signal back to the radar receiver. The reflected signals or echoes from chaff, cloak the presence of the aircraft by cluttering the radar screen with false targets. The chaff is thus used to jam radar signals and prevent a threatening radar target from being distinguished from decoy targets created by the chaff.
Many guided missiles are equipped with radar seekers capable of detecting specific targets and locking the guidance system to home in on that target until impact of the missile with the target occurs. The target may be another missile, an airplane, a ship, a tank, or any other target that can be identified by a radar image. The potential target may counter the threat by deploying a chaff cloud around the enemy radar, thereby rendering the radar scanner ineffective. When a cloud of chaff is positioned between the radar seeker and the intended target, the target is effectively shielded behind the chaff and cannot be identified by the attacking missile.
Incoming mortar fire can be tracked by radar and the mortar location can be pinpointed for return fire. Scanning radar will reveal its own position to any passive radar receiver. Chaff-dispensing mortar rounds, deployed near the seeking radar, may prevent the radar seeker from finding the mortar location. Chaff dispensing gun projectiles may be used to jam radar seekers at intermediate ranges and chaff dispensing rockets may be used to jam radar at greater ranges. The air defense systems of major targets may be effectively neutralized by enveloping the target in chaff dispensed by bombs, rockets, gun projectiles, mortars or combinations thereof, until the target has been destroyed.
Chaff interdiction is an effective electronic countermeasure against radar, guided missiles and radar-directed fire-control systems which direct the firing of guns and mortars. However, efficient, reliable, versatile dispensing and dissemination systems for chaff payloads have heretofore presented a variety of problems. In prior art dispensers, chaff bundles are routinely ejected to the rear of a combat aircraft when its aft scanning radar detects signals of a potential threat. The chaff bundles are ejected by explosive charges which direct their force along the longitudinal axis of the bundle. Unfortunately, explosive expulsion may not adequately release the chaff from its outer wrapper. The explosive shock may break fiberglass strands from which the individual chaff dipoles are formed. The expelling gases may not adequately disseminate the tiny strands of chaff as individual electrical dipoles. The superheated combustible gases produced by the explosive compound, may not ignite when mixed with atmospheric oxygen. The aluminum or other metallic coating on one micron diameter dipoles engulfed in the fuel-air combustion process, may ignite in the presence of atmospheric oxygen and nitrogen to form aluminum oxide or aluminum nitride, both of which, being electrically nonconductive, would preclude proper functioning of the chaff dipoles. The axial explosive loading may crush the bundle of fibers into a matted "bird's nest" which would, of course, prevent the proper dissemination and distribution of the dipoles to operate as intended.
The nature of such problems encountered in the prior art is better understood by acquaintance with the nature of the chaff material. A chaff dipole usually consists of an aluminum-coated fiber of boro-silicate glass having a specific length corresponding to the wavelength of the radio frequency of the enemy's radar or other detection device. Dipoles of this composite material are produced in diameters of one micron or less. A single dipole of chaff is difficult to see by the unaided eye. A chaff bundle having a cross-section of one square inch contains approximately five hundred thousand such dipoles. If these dipoles are, for example, one inch in length, the volume of one cubic inch of such dipoles weighs about 0.0375 pounds. Thirteen million such dipoles would weigh less than one pound.
The surface area of a pound of dipoles is on the order of 115 square feet. Accordingly, a dipole has very little mass and very high surface area. These characteristics of chaff dipoles allow the cloud of dipoles to float or to remain suspended in air for long periods of time and they are made this way for that very purpose. However, their design prevents them from being accelerated by explosive forces because they have no significant mass to store kinetic energy and their large specific surface area generates a great deal of aerodynamic drag so that any stored kinetic energy is quickly dissipated before the dipoles can travel for any significant distance through the atmosphere.
Still another problem associated with dissemination of chaff is electromagnetic attraction between the dipoles. The fiberglass strand is an electrical insulator and it is coated with a microscopic film of aluminum. When an insulator is coated with a conductor, it is capable of accumulating and holding a capacitive charge of static electricity. The electrically-charged fiber becomes an electromagnet with positive and negative polarities. Hence, it is called a dipole. Due to the low mass and high specific surface area of this material, the magnetic attraction between dipoles of opposite charge represents a force of significant magnitude between the chaff dipoles which must be overcome during dispensing and dissemination.
Accordingly, there has been a long felt need for a chaff or other payload dispensing and disseminating system which reliably releases the chaff from its wrapper; which will not break the fiberglass strands into multiple fragments; which will reliably disseminate the tiny strands of individual dipoles; which will permit the complete combustion of the gases used for disseminating the dipoles; which will not result in the ignition of the aluminum coating on the surface of the dipoles; which will not crush the bundle of fibers into a matted bird's nest; and which will assure the uniform, broad distribution of the chaff dipoles quickly and efficiently overcome magnetic attraction between the oppositely charged poles of the individual dipoles of chaff.